Shock sensors are widely used in automobiles to detect the onset of a crash. Typically the magnitude and direction of the crash are sensed by micro-mechanical devices that are fabricated as part of an electronic chip. However, integrated circuit chips and micro-mechanical devices are subject to electromagnetic interference, with the result that sometimes a crash is indicated when no crash event is taking place. Macro scale mechanical shock sensors are employed as a safety device to provide a positive indication that the crash of a given magnitude is occurring. With the assurance that a crash is actually taking place the electronics associated with the micro-mechanical shock sensors can determine the magnitude and direction of the crash and deploy various safety systems in accordance with predetermined or adaptive logic.
Reed switches are often employed in the construction of mechanical shock sensors because of their extreme reliability, low-cost and relatively high current switching capabilities. Reed switches are also hermetically sealed from the atmosphere that contributes to their reliability and makes them suitable for use in hostile environments. Existing shock sensors often employ a second hermetic seal about a shock sensing mass and spring in order to form a shock sensor protected from the environment.
What is needed is a shock sensor which has the reliability of a reed switch and which provides an improvement in cost and packaging size.